If you have just started to experiment with photography, are enjoying it, have a good camera like your GR, and have an important trip coming up, I would recommend that you invest in some photography education rather than a new camera at this point. My husband and I took an introductory course (6, 2-hour lessons) a few years ago before a big trip to Borneo and it was one of the best investments of time and money we ever made in terms of enhancing our travel experience.
You may be able to find a course locally, and I recommend a hands-on course if it's available, since the teacher can help you with your camera's operation if you encounter difficulties.
But if that's not practical, I would recommend the online photography school run by Bryan Peterson at ppsop.com. I've taken half a dozen courses through this school and I like the format. Most of them (except the introductory course, Understanding Exposure, which is 8 weeks long) are 4 weeks long and cost $169. You get a weekly lesson (or series of videos) to watch, a homework assignment to complete and an online discussion forum to interact with the teacher and students. The teacher reviews and gives feedback on your homework and you can see his or her feedback on the other students' work as well, so you learn from what they do as well as what you do.
As I mentioned, there is an 8-week course based on Peterson's book, Understanding Exposure, and it will teach you a lot about how to operate your camera in manual mode. It's designed principally for people with DSLRs, but I think you could still learn a lot that is applicable to your GR, since it has manual mode.
Another possibility is the shorter and less expensive Travel Photography course taught by Alan Thornton. It's $169 and 4 weeks long. I took his advanced course and liked him as a teacher. It's here:
Travel Photography
Classes start each month on the first Friday (so they start this Friday), with homework usually due 9 days after the assignment is released.